Motoscrubs.com

Sooo.

Perhaps I should have joined the forum a long while since but hey, I have been around classic/vintage motorcycles +/- 45years thats my excuse.
Many years ago I got hold of a 450 via a very good friend in the US, I’d always wanted one especially as I still have my first real bike a 250mk3.
Anyway long story short what I ended up with was a 450desmo in an SCR frame but it came also with an RT frame that had been “hacked around” and a whole load of RT cycle parts BUT no front end.
I know nothing of the bikes history but my guess is from the cracked and damaged RT side panels it had been used for at least one competition.
With a whole lot of other projects I decided to casually and sporadically look for parts to make a complete RT rolling chassis. I had only ever seen one other in real life and man they looked real nice anyway that took … checks notes …. 27 years.

A few months ago the final parts arrived and I now have a complete rolling chassis. My original plan was to check the engine but TBH it looks and feels pretty good except that the cable from the Dy-mag was cracked brittle and what was left of the wire core was green copper oxide.
I figured the wiring was pretty simple.

What a mistake that was.

So here I am. Some of the threads on the site are quite old and for all the reading I am wiser but not confident.
What I have is an early bike, the engine # sits between 70/71 according to the BH number register while the frame has no number or stamping obviously the foil sticker is long gone and so putting this as a Berliner model.

I have no need for a road bike so decided that I didn’t need any lighting kit.

I stripped out the dy-mag stator and it has/had two wires both yellow but reading the threads I concede one may well have been white? The local electrical rewinders found two matching wire sizes and they are now Brown and Blue.
Using my tester set on 200Ω one winding reads 1.5 to ground the other reads 0.9 to ground.

I also replaced the black/white wire from the points/condensor/adv unit.

The only other thing the bike had was a 6v coil stamped on the bottom Ducati elettrotecnica 3211106 6Vca 15 11 20 and the top marked Ducati elecrotecnica with the two terminal poles marked #1 and #15

The reading between the two poles again using the 200Ω setting reads 5.6 and with no reading between the HT lead and either pole or the body

Oh and a kill switch which is not I think a Ducati item

So here is my quandary:

If I understand all the different posts here:

One of those stator wires is for the spark/coil and one is for “electrics”
2. The coil markings are :
15 = switched battery feed
1 = connection at the coil (in this case, to ground).

If the wire from the dymag stator plate,( I take it the one with the lowest resistance goes to the pole marked 15 on the coil) and the wire from the points/condenser/adv unit goes to the pole marked 1
(I take it the kill switch also goes to the coil pole marked #1)

Where the hell does the other wire from the dy-mag windings go? OR does it indeed need to go anywhere?

If some one would help what is the obvious bit I am missing of the puzzle?

Hi Adrian

here the RT wiring diagram . the RT alternator has 2 coils and a flywheel with 4 magnets .
you have to time that flywheel to
most other widecase engines have a 3 wire alternator
2 yellow and 1 red wire

a RT has a ac coil . that coil has a green tag on it

Eldert

and here the flywheel positions

Eldert

[quote="Adrian"]

The reading between the two poles again using the 200Ω setting reads 5.6 and with no reading between the HT lead and either pole or the body

For the HT lead terminal, I think you may need to put your meter on a different range? Most coils have a few ohms on one side and a few thousand on the other.

i allmost forgot the RT uses another automatic advance unit to i has AA 367 B stamped on it

it advances 18 degrees and has a diff cam to to saturate the AC coil

Eldert

Many Thanks Eldert
I have seen that wiring diagram previously but it didn't appear to help.
It shows the Red wire going to a lighting switch that feeds both a front and rear light.
As my bike has neither light my best guess was that lead remains redundant ?
If I understand the history correctly the first bikes where imported as "competition bikes" for the then growing US sport of desert racing. Presumably and from early pictures these had no lighting.
With the colour of the original wires being different I wasn't sure if the specifically first batch of bikes had a different Dy-mag configuration/design and that second wire went elsewhere? Otherwise the whole winding and wire appears redundant which would seem odd for a competition bike that took so long to get from design to conception?
From what I have understood (perhaps mistakenly) it wasn't until later that a lighting /road kit became available as an option which is when I guess the second wire could be used or would the lighting kit have required a different stator plate and flywheel? There doesn't appear to be much information available about those early Berliner bikes.
So far I haven't tried to see if I can get a spark but hopefully in the next couple days I will connect the wires up leaving what I assume (thats dangerous in itself) the lighting wire redundant and see if I get anything.
Yes I saw the auto advance unit when I removed the points plate to replace that wire I didn't make a note of any marking on it but next time I take out the back plate I will have a closer look.

Many thanks Ranton Rambler I will have another look at the coil later tonight. My guess is if that an original coil (I don't see either colour label on it but it is stamped on the bottom as a 6V AC coil ) then its been sitting around for a longtime and whilst there is no reason for them to degrade if kept in good conditions I have no idea about its first 25 years of life. I made the two measurements based on something quoted on one of the threads I read here about the difference between AC and DC coils.

Another couple of thoughts:

How do you know any of the electrical system is original by now? My 175 had a proper mish-mash of bits so I chucked it all away except the generator and made a new loom with an Electrex 12V reg-rec and 12V coil.

My generator had 2 yellow wires, but the 2 coils have identical resistances and I think are connected in series. As it looked good I left it all alone except for insulating the central connection from ground which is recommended for 12V operation.

If you have a standard coil lying around, could you slave it up from a battery and get it running? You could then see what is coming out of the 2 wires.


I have my old 6V coil, so will try and remember to check what it says on it.

Ian

The only other thing the bike had was a 6v coil stamped on the bottom Ducati elettrotecnica 3211106 6Vca 15 11 20 and the top marked Ducati elecrotecnica with the two terminal poles marked #1 and #15.

I appears you have an AC system. The 6Vca (corrente alternata/current alternating) stamping on the coil shows this. That coil should test approx. 4 ohms between the outside terminals (primary winding) and 11 k ohms between the outside and central terminal (secondary/spark winding).



In my Clymer manual the RR has three stator wires as inputs and two wires coming out. One goes to the battery, and the other goes to the ignition coil. I assume the wire that goes to the battery is rectified and runs the lights and horn. The second wire goes to the AC ignition coil.

Many thanks for the help to date;

I rechecked the coil and it does have 12.4KΩ between the HT and both pole terminals.
So thats good then?

With regard to how do I know if anything is original, apart from the 6V AC coil which is anyones guess there is only the Dy-mag, no lights no loom nothing. Engine wise I have two other bikes that I know have never had a spanner put to them (XR1000 and XLcr1000 if anyone is interested) and there are pretty good indications compared to my other bikes that have all been "worked on". So I am pretty sure that this engine has never had a spanner on it ..until now when I stripped the primary to pull the clutch/flywheel etc to get access to the stator plate to remove it to replace the two wires.
I know there are lots of threads that say that it should have three wires but i promise, there is no hidden or missing third wire. The stator plate had only two yellow wires exiting the casings. I concede one of those may have originally been white or had a white strip on it that degradation rendered yellow.
Having stripped the frame to repair a damaged rear seat loop I can attest that there are no missing brackets and definitely no mounting for a battery tray. According to literature of the era the original 400 RT's ordered by Berliner were for competition bikes to take on the mighty BSA500 goldie scrambler and had no lighting but later had an optional lighting kit.
A Cycleworld test from 1971 says they didn't even have a kill switch and no ignition switch so stopping was via the decompression lever.

So my remaining question is still where did the two wires from the dymag go. Obviously one went to the coil but what about the second wire? Did it remain redundant until required for a possible future lighting kit or did it have a more elegant terminal. What happens if it too went to the coil?